Modern dumbbells have a long and interesting history. The earliest record of a dumbbell was the stone "haltere" used by the ancient Greeks and Romans to train their long jumpers. They were carried and dropped at lift off, and it was thought that the sudden release of the haltere resulted in the athlete jumping a greater distance.
During the 1700's and 1800's the wooden Indian club (pin) was popular as a gentlemen's physical culture device. These clubs were available in different weights and like the modern fixed weight dumbbell, were complete with a rack for storage. The heaviest Indian club was approximately thirty-five pounds. Considering that the athlete always grasped the club at its end, the use of a thirty-five pound pin was quite a demonstration of fore-arm strength.
The advent of the modern strongman in the late 1800's saw the development of the kettle bell. Like the Indian club, this bell forced the athlete to grasp an unbalanced weight resembling a bowling ball with a handle. Considerable skill, balance and strength was required to lift a kettle bell, the heaviest of which was in the 200-300 pound range.
Early balanced iron dumbbells became available after the turn of the century, with adjustable dumbbells being introduced by Milo Stanborn just before World War II.
Today, dumbbells are generally recognized as the most efficient of strength training devices. They allow extreme flexibility in patterns of movement and permit the athlete to perform a real world training regimen unlike, for example, bungee cord exercises. Therapists like to utilize dumbbells because they reflect everyday movements and their flexibility allows the patient to train around joint and muscle trauma. Athletes that train with dumbbells enjoy productive gains not available with other training modalities because they require balance and involve synergistic muscle groups to contract during the lift. The necessity to balance the dumbbells and coordinate movement of each hand stress the muscular and nervous system unlike any machine exercise. With machines, a portion of the athlete's musculature can actually relax due to the absence of fully balanced coordination; i.e., one side can push harder than the other.
There are two basic forms of dumbbells: fixed or "pro-style", and adjustable dumbbells. Fixed dumbbells are individually compact, but are typically sold in sets which must be stored on a rack that is bulky and cumbersome. Adjustable dumbbells have historically incorporated plates and locking collars secured to the ends of an extended handle.
Adjustable dumbbells are the most space and cost efficient exercise equipment, however, they are not without some drawbacks. One drawback is the time it takes to change or adjust both dumbbells. Removing and replacing the locking collars and plates is time consuming, and can be a potential safety hazard if the collars are not securely tightened. Another drawback is that it is difficult to perform a "kickup" due to the protruding end of the handle. Some exercises such as bench presses, inclines and shoulder work typically begin and end with the dumbbells resting on the knees of the athlete, however, this can be unwieldy and painful if the ends of the dumbbells are not relatively flat.
Various adjustable dumbbells have been developed heretofore. U.S. Pat. Nos. 4,948,123 and 4,566,690 to Schook, 4,913,422 to Elmore et al, 4,900,016 to Caruthers, 4,880,229 to Broussard, and 4,743,017 to Jaeger are representative of the prior art in this regard. Each of these references, however, addresses only certain aspects of an adjustable dumbbell, such as releasability, interlocking of the weights, etc.
There is still a need for an adjustable dumbbell of improved construction which is not only compact in size, but also easily and securely adjustable and comfortable to use without the clutter of loose weights.